The Chemical Weapons Convention was adopted by the Conference on Disarmament in Geneva on Sep. 3, 1992, entered into force on Apr. 29, 1997, and calls for a prohibition of the development, production, stockpiling and use of chemical weapons and for their destruction under universally applied international control. Eliminating the hazard of chemical warfare agents is desirable both in storage sites and on the battlefield. Decontamination of battlefields requires speed and ease of application of decontaminant. Surfaces involved pose a challenge for decontamination techniques since some surfaces absorb such agents, making decontamination difficult. Examples of surfaces that could be involved include those of tanks, ships, aircraft, weapons, electronic devices, ground, protective clothing and human skin. The decontaminants should not be corrosive, so that surfaces are not damaged during/following decontamination. An optimum solvent of a decontaminating method should provide ease of application, solubility of the chemical warfare agent, non-corrosiveness, and minimal environmental contamination. Since the establishment of the Convention, considerable effort has been directed toward methods of facilitating the controlled decomposition of organophosphorus compounds.
Aqueous decontamination systems, such as hydrolysis systems, have been used in the past, most notably for nerve agents, particularly for the G-agents tabun (GA), sarin (GB), soman (GD) and GF. However, hydrolysis reactions are not suitable for all chemical warfare nerve agents such as V-agents VX (S-2-(diisopropylamino)ethyl O-ethyl methylphosphonothiolate) and Russian-VX (S-2-(diethylamino)ethyl O-isobutyl methylphosphonothiolate), whose decontamination chemistries are very similar to one another (Yang, 1999). The V-agents are about 1000-fold less reactive with hydroxide than the G-agents (due to their poor solubility in water under basic conditions), and they produce product mixtures containing the hydrolytically stable, but toxic, thioic acid byproduct.

Although some chemical warfare agents are water soluble, they may be applied in combination with a polymer so that, being thickened, they adhere well to surfaces. These “thickened” agents are only minimally soluble in water. In the case of decomposition using a hydrolysis reaction, products in which a phosphorus-sulfur bond is preserved are common; these are toxic in their own right and are relatively resistant to further reaction. Another disadvantage of an aqueous decontamination system is that hydrolysis reactions are not catalytic, and therefore require stoichiometric amounts of reagents. Furthermore, commonly used aqueous methods, due to their alkaline pH, are not suitable for decontamination of human skin. Yet another disadvantage of aqueous decontamination methods is the caustic wastewater produced as an end product, which poses a challenge for disposal.
Historically, decontamination of chemical warfare agents has been effected using hydrolysis or oxidation using bleach or alkali salts. Bleach is corrosive to skin, rubber, and metal surfaces and is ineffective in cold weather conditions. Alkali salts require excess hydroxide ion in order for the reaction to go to completion rapidly, thus resulting in a caustic product. Non-catalytic methanolysis of V-agents has been studied, wherein the reaction of VX with alkoxide leads primarily to a displacement of the SR− group (Yang et al., 1997).
Transition metal ions and lanthanide series ions and certain mono- and dinuclear complexes thereof are known to promote hydrolysis of neutral phosphate and/or phosphonate esters. However, the available literature on the hydrolysis of phosphothiolate (P═S) esters and phosphothiolates is quite sparse with only the softer ions such as Cu2+, Hg2+ and Pd2+ showing significant catalysis. The lack of examples may be due to reduced activity of P═S esters, their poor aqueous solubility and the fact that anionic hydrolytic products bind to the metal ions thereby inhibiting further catalysis.
There is a need for a viable catalytic decontamination method which is inexpensive, has high catalyst turnover, and occurs at relatively neutral pH and ambient temperature, and most importantly, proceeds rapidly, e.g. t1/2<1 min.